The present invention relates to the improvement for a fluidized bed polymerization reactor. More particularly, it relates to the improvement for a flow deflector at the bottom of a fluidized bed polymerization reactor.
When an exothermic polymerization reaction is conducted in a fluidized bed reactor, the reaction rate is to be restricted so as to have time enough for removing the released heat from the fluidized bed. A method to raise the removal rate of the reaction heat is to compress and cool the gas in a monomer state that is needed to recycle back to the reactor so that it is partially condensed. The liquid generated is entrained by the recycle monomer gas stream and returns to the reactor together with the gas stream. This is referred to as the xe2x80x9ccondensing modexe2x80x9d operation of a polymerization reaction. U.S. Pat. Nos. 4,543,399 and 4,588,790 to Jenkins et al. disclose this operation method, which point out that this xe2x80x9ccondensing modexe2x80x9d operation allows a reduction in the temperature of the recycle gas stream and that the evaporation of the liquid requires absorption of heat. The combination of the two functions allows much higher space-time-yields in this mode than those in thexe2x80x9cnon-condensing modexe2x80x9d.
The above operation modes both require the use of different inlet devices of the reactor, therefore the reactor has to be shut down for converting the inlet device when the interchange between the two operation modes is required. To solve this problem and further raise the productivity of the fluidized bed reactor, Chinese Patent Application No. 85106978 to UCC of U.S.A discloses a novel reactor inlet device-flow deflector. This flow deflector is installed under the distributor plate of the fluidized bed reactor and provides two fluid flow paths for the fluid to enter the mixing chamber, a first fluid flow path along the wall of the mixing chamber and a second upwardly fluid flow path. The preferred flow deflector is an annular flow deflector, having aperture for providing a central, upwardly oriented fluid flow path. Besides, it also provides a peripheral fluid flow path around the flow deflector and along the wall of the mixing chamber. It is claimed that during the operation of the flow deflector with such a structure, the build-up of the solid particles and the agglomeration of the liquid in the mixing chamber is prevented by sweeping the wall of the mixing chamber with the gas stream entering through the annular outer second fluid flow path peripherally around the annular flow deflector. As shown by the arrows in FIGS. 1 and 2 of this literature, the central upward gas stream is mixed with the peripheral gas flow and thereby a more uniform distribution of any liquid and/or solid in the gas flow is guaranteed.
However, according to our practice in many years"" operation of this kind of annular flow deflector commonly adopted by the Unipol fluidized bed polymerization reactor imported from UCC, we found that this kind of flow deflectors have the following disadvantages when operated in the condensing mode:
1. Gas is non-uniformly distributed. The flow of the central gas flow is so great, and the velocity is so high that the recycle stream and the powders and liquid entrained by the stream lash directly at the lower surface of the distributor plate. If the recycle stream entrains polymer lumps, the polymer lumps smaller than xcfx8616 mm would enter the holes of the distributor plate under the action of high speed stream and result in plugging. By contract, the velocity of the stream within the annular zone 500 mm from the periphery of the distributor plate along the radius direction would reduce, resulting in plugging in the distributor plate due to the frequent deposition of powders.
2. Deposited powders are likely to agglomerate into flakes. Because the area of the upper surface (i.e., the opposite of the flow direction of the recycle stream) of the flow deflector is relatively large and the stream flows through the central hole and the peripheral path of the annular flow deflector respectively, so the zone above this surface is a dead xe2x80x9czonexe2x80x9d and powders often deposit. When the temperature of the inlet stream is high enough for the powders to soften and stick, flaky polymers with the same area as that of the upper surface of the annular flow deflector would form. When the reactor is operated in the condensing mode, these flakes fall off due to impact and soak by liquid and then lash at the distributor plate after being crushed by the impact of the stream, resulting in plugging.
3. The range of the amount of the condensing agent is narrow. For this kind of flow deflector, the amount of the condensing agent is restricted to a range of 3xcx9c10 wt %. This kind of flow deflector is not suitable to a greater amount of condensing agent.
Therefore, the present invention makes a bold improvement in the structure of the flow deflector. It is proved by the practical application that the flow deflector of the present invention has completely overcome the above disadvantages of the flow deflector in the prior art. Safe and stable operation is realized with a liquid content of the recycle stream in the range of 3xcx9c25 wt %. Because the amount of the condensed agent increases, the heat removal increases, so that the space-time-yield can further increase to 200% of the originally designed capacity.
For this reason, the present invention provides a novel fluidized bed reactor, which comprises:
d. a distributor plate under the fluidized section of the reactor;
e. a mixing chamber formed by confining the reactor space under the distributor plate with said distributor plate; and
f. a flow deflector installed under the distributor plate and at the entry of the reactor bottom, characterized in that the flow deflector comprises an annular plate and a conic plate,
the annular plate being positioned above the reactor bottom entry with a hole diameter of D1 by spacers, the said annular plate having a central hole with a diameter of D2; and
the conic plate being located above the annular plate, concentric with the annular plate and supported on the annular plate by spacers, the conic plate being a reversed cone with a cone angle of a to the horizontal plane and having a central hole with a hole diameter of D3;
the minimum section area between the annular plate and the reactor bottom being S1, the minimum section area between the annular plate and the conic plate being S2, and the circular area of the central hole of the conic plate being S3;
the flow deflector being adapted to provide at least three paths for the gas stream to enter the mixing chamber, i.e., a first upwardly fluid flow path through the entry D1 of the reactor bottom and section S1 and along the wall of the mixing chamber, a second upwardly fluid flow path through the central hole D2 of the annular plate and section S2 below the conic plate and towards the side wall, and a third upwardly fluid flow path through the central hole D3 of the conic plate.